Heroku and 123 Reg showing IIS page only on naked domain

I've got a site set up with SSL that works as expected when manually typing in 'https://example.com' or 'http://example.com'.

However, when I navigate to just 'example.com' I get an IIS hosting page.

My DNS is set up through 123-reg and my site is hosted on Heroku.

AFAIK Heroku is a Linux-based server system so I'm genuinely confused where an IIS page would be coming from. It's not running any of my code when inspecting element and logging things out to the console.

It's just an IIS image.

My DNS records are as such:

@ CNAME example.com.herokudns.comwww CNAME www.example.com.herokudns.com

I also am using express-sslify to redirect to HTTPS however as my code isn't being run on the naked domain it's not able to redirect traffic.

Any ideas?